The present invention relates to the use of an apertured oleophilic endless sieve wrapped around the cylindrical apertured wall of a rotating cage to separate a mixture of oil phase and aqueous phase in a separation zone. More particularly, this invention relates to a process wherein both phases tumble in the cage, pass through the apertured cylindrical cage wall to the surface of the apertured oleophilic endless sieve where aqueous phase, which may include hydrophilic solids in particulate form, passes through the sieve apertures and oil phase is captured upon contact by the surface of the apertured oleophilic endless sieve in a separation zone. The sieve and cage revolve continuously such that the captured oil phase is continuously carried by the endless sieve into a recovery zone where the oil is removed from the sieve. Separation in the separation zone generally is carried out at a relatively lower temperature and removal of oil phase in the recovery zone generally is carried out at a relatively higher temperature to take advantage of the stickiness of the oil phase at relatively lower temperatures and the fluidity of the oil phase at relatively higher temperatures. The actual temperatures used are selected largely according to the properties of the oil phase.
This invention is concerned with recovering bitumen from mined oil sand (tar sand), from oil sand tailings, middlings and sludge ponds and for the recovery of oil phase from oil field sludges, oil-sand-water mixtures, emulsions, heavy oil and water mixtures and the like. Extensive deposits of oil sands, which are also known as tar sands and bituminous sands, are found in Northern Alberta, Canada. The sands are composed of silicious material with grains generally having a size greater than that passing a 325 mesh screen (44 microns) and a relatively heavy, viscous petroleum called bitumen, which fills the void between the grains in quantities of from 1 to 21 percent of total composition. (All percentages referred to herein are in weight percent unless noted otherwise.) Generally, the bitumen content of the sand is between 5 and 15 percent. This bitumen contains typically 4.5 percent sulfur and 38 percent aromatics. Its specific gravity at 16.degree. C. ranges from about 1.00 to about 1.06. The oil sands also contain clay and silt. Silt is defined as silicious material which will pass a 325 mesh screen (45 microns), but which is larger than 2 microns. Clay is material smaller than 2 microns, including some siliceous material of that size. Extensive oil sands deposits are also found elsewhere in the world, such as in the Orinoco heavy oil belt of Venezuela, in many of the African countries, in Russia and in the state of Utah. The mineral and bitumen of these deposits vary from place to place. For example, compared with the Alberta oil sands, the Utah tar sands contain a coarser sand, less clay, less water and an even more viscous bitumen.
Much of the world resource of bitumen and heavy oil is deeply buried by overburden. For example, it has been estimated that only about 10 percent of the Alberta oil sand deposit is close enough to the earth's surface to be conveniently recovered by mining. The remainder is buried too deeply to be economically surface mined. Hydraulic mining or tunnel mining has been proposed for these deeper deposits. Generally, however, it is considered that enhanced recovery by steam injection, by injection of aqueous solutions, and/or by in-situ combustion may possibly be more effective for obtaining bitumen or heavy oil from deeply buried formations. Such enhanced recovery methods use one or more oil wells that penetrate the formation and stimulate or recover the resource. Recovery of bitumen from a well by steam stimulation, for example, is described in Canadian Patent No. 822,985 granted on Sept. 16, 1969 to Fred D. Muggee. Depending upon the procedure employed, enhanced recovery methods either produce mixtures of oil and water, water in oil emulsions or produce oil in water emulsions.
There are several well known procedures for separating bitumen from mined oil sands. One such method is known as the "Hot Water Process." In a hot water method, such as disclosed in Canadian Patent No. 841,581 issued May 12, 1979 to Paul H. Floyd et al, the bituminous sands are jetted with steam and mulled with a minor amount of hot water and sodium hydroxide in a conditioning drum to produce a pulp which passes from the conditioning drum through a screen, which removes debris, rocks and oversize lumps, to a sump where it is diluted with additional water. It is thereafter carried into a separation cell.
In the separation cell, sand settles to the bottom as tailings which are discarded. Bitumen rises to the top of the cell in the form of a bituminous froth which is called the primary froth product. An aqueous middlings layer containing some mineral and bitumen is formed between these layers. A scavenging step is normally conducted on this middlings layer in a separate flotation zone. In this scavenging step, the middlings are aerated so as to produce a scavenger tailings product which is discarded and a scavenger froth product. The scavenger froth product is thereafter treated to remove some of its high water and mineral matter content and is thereafter combined with the primary froth product for further treatment. This combined froth product typically contains about 52 percent bitumen, 6 percent mineral matter, 41 percent water, all by weight, and may contain from 20 to 70 volume percent air. It resembles a liquid foam that is difficult to pump and, for that reason, is usually treated with steam to improve its flow characteristics.
The high water and mineral contents of the combined froth product normally are reduced by diluting it with a hydrocarbon diluent such as naphtha. It is then centrifuged to produce a tailings product and a final bitumen product that typically contains essentially no water and about 1.3 percent solids and that is suitable for coking, hydrovisbreaking and other refining techniques for producing a synthetic crude oil. The tailings products, containing some naphtha, are discarded.
There are basically four effluent streams from the Hot Water Process. Each carries with it some of the bitumen of the feed; thereby reducing the efficiency of the Process. These include the oversize material, the sand from the separation cells, the silt and clay from the scavenger cells and the tailings from the centrifuges. Up to 30 percent of the bitumen in the original feed and up to 5 percent of the naphtha stream may be lost in this manner. Much of this bitumen effluent finds its way into large retention ponds that are typical of the Hot Water Process. The bottom of such retention ponds may contain up to 50 percent dispersed mineral matter substantially of clay and silt as well as 2 to 10 percent bitumen. As disclosed in Canadian Patent No. 975,697 issued on Oct. 7, 1975 to Davitt H. James, this part of the pond contents, referred to as sludge, is a potential source of bitumen.
The Hot Water Process described in the preceding paragraphs separates bitumen from a slurry prepared from mined oil sand. The slurry is hot, contains finely dispersed air bubbles and the bitumen is in the form of small flecks. Such a slurry is amenable to subsequent separation in the hot water bath, after dilution, wherein bitumen forms into a froth that rises to the top of the bath and is skimmed therefrom. Alkaline reagents such as sodium hydroxide are normally added in this process to give the slurry those properties that provide for efficient flotation of the bitumen in said water bath. However, in the presence of sodium hydroxide, fine clay particles in the effluent streams from this process do not settle readily. For this reason inordinately large settling ponds are required to contain the effluents from commercial hot water oil sands extraction plants.
When bitumen or heavy oil is produced from deeper formations, such as by steam stimulation or by in-situ combustion, the oil produced at the production wells is a mixture with water in emulsified form that may vary in composition from 1 to 99 percent oil. Some of these emulsions readily separate, but other emulsions are extremely stable and very difficult to break. Separation by gravity becomes particularly difficult to achieve when the oil (bitumen) of these mixtures has a specific gravity approximating that of water, i.e., close to 1.00. Quite often a chemical demulsifier and a diluent are added to break and separate these emulsions. The demulsifier conditions the emulsion so that it can be separated and the diluent acts to dissolve the suspended oil of the emulsion and make the combined oil phase light enough so that it can be separated by floating the oil off the top of the water phase. Treaters are used quite often to speed up the separation process. Such treaters may be in the form of coalescers where the diluted emulsion is made to flow through a packed bed or through a sponge to enhance subsequent gravity separation or in the form of electrical precipitators. Treater operation becomes difficult when the emulsions contain particulate solids such as sand, silt or clay. These solids tend to form pads in the treaters which interfere with the emulsion separation process. Such pads periodically must be flushed out of the treaters to adjacent desand pits where the solids are allowed to settle and part of the fluid is pumped back into the treater. The resultant solids, oil and water mixture are removed by vacuum trucks and/or back hoes and are disposed off by spreading it on gravel and dirt roads in the vicinity to keep down the dust. However, the amount of discard oil that needs to be disposed off in this manner is becoming much in excess of the requirements of the roads in the area and other uses must soon be found or improvements in technology are required to prevent the production of such effluents and to make more effective use of the available oil.
Not only does current emulsion separation technology suffer from operational difficulties when separating emulsions that contain particulate solids, but also the requirements of large amounts of diluents for the separation and the attendant loss of diluent with the effluents is a problem of economics and environmental pollution.
The present invention applies to processes that get away from the gravity separation of the prior art and utilizes apertured oleophilic endless conveyor sieves to achieve slurry and/or emulsion separations. The present invention is an improvement on certain related processes utilizing an apertured oleophilic drum or belt for oil phase separation that are disclosed in the inventor's U.S. Pat. Nos. 4,224,138; 4,236,995; 4,392,949; 4,405,446; 4,635,860 and 4,511,461, which are discussed further on in these specifications to describe the improvements claimed herein.